The present invention relates to flotation devices of the type used in mineral separation, and more particularly to flash flotation devices.
Flash flotation cells are well known, and typically comprise a tank to receive and contain slurry from a grinding mill, cyclone separator, or the like. An agitator, comprising a rotor housed within a stator, is normally disposed within the tank to agitate the slurry. An aeration system is also provided to direct air under pressure into the agitator through a central conduit formed within the drive shaft. As the bubbles from the aeration system rise toward the surface of the tank, they carry with them floatable particles which form a mineral enriched surface froth. The froth then migrates over a lip and into a launder whereby the floatable particles suspended in the froth are removed from the cell as mineral concentrate. Coarser and denser particles fall from suspension, for removal through a discharge outlet formed in the bottom of the tank. An automatic control system, typically incorporating a liquid level sensor and a PID controller, regulates a control valve in the bottom discharge outlet, to maintain a constant liquid level in the tank.
In the past, however, problems have arisen in regulating the flow through the bottom discharge outlet, because most conventional valve assemblies are incapable of accommodating coarse material of the type which typically emerges from grinding mills.
In an attempt to address this problem, it has been common practise to use pinch valves. These essentially comprise a flexible tube or sleeve positioned in a fluid pipeline and adapted for compression between opposing pinch bars to provide progressive regulation of fluid flow through the pipeline. Such valves are typically more accommodating of larger particles than most other types of valve because of the flexibility of the sleeve. However, even with pinch valves, rapid wear is caused by the coarse and often jagged particles. This problem is exacerbated when the valve is used for control purposes because the flow is both fast and turbulent. This necessitates frequent replacement of the pinch valve sleeves. Aside from the ongoing sleeve replacement costs, the associated downtime has a considerable adverse affect on the efficiency of the plant as a whole.
It is therefore an object of the present invention to overcome or substantially ameliorate at least some of these disadvantages of the prior art.